1. Field of the Invention
This invention relates to catalysts comprising one or more transition metal oxides supported on a silica-containing support, the silica content of which is less than 50 wt.% thereof. More particularly, this invention relates to solid acid catalysts comprising a catalytic metal oxide component wherein said metal is selected from the group consisting essentially of (a) tungsten, niobium and mixtures thereof and (b) mixtures of (a) with tantalum, hafnium, chromium, titanium, zirconium and mixtures thereof, supported on a silica-containing inorganic refractory metal oxide support, the silica content of which is less than 50 wt.%.
2. Background of the Disclosure
U.S. Pat. Nos. 4,269,737, 4,233,139 and 4,244,811, the disclosures of which are incorporated herein by reference, disclose solid acid catalysts comprising certain supported transition metal oxides, their preparation and use as acid cracking catalysts. The supports are silica-free refractory metal oxides which are not in themselves acid cracking catalysts, but which when combined with the transition metal oxide component result in acid cracking catalysts. These catalysts are taught as having enhanced activity and selectivity towards forming liquid products compared to conventional acid catalysts. They also exhibit remarkable resistance to coke make and have unusual steam stability. In fact, in some cases it is preferred to pre-steam these catalysts prior to use in order to stabilize the surface thereof. Although steaming these catalysts initially results in a decrease of both surface area and strong acid sites, the steaming itself serves to stabilize the remaining surface area and acidity which is not substantially adversely affected by subsequent steaming. The catalysts described in these patents exhibit primarily Lewis acidity.
U.S. Pat. No. 2,849,383 discloses silica-alumina cracking catalysts which may contain tungsten oxide as a component thereof, which catalysts are steamed at a temperature of from about 600.degree.-800.degree. C. prior to use. However, the disclosures of this patent are very specific in teaching that the silica content of the catalyst support should be at least above about 50% silica calculated as SiO.sub.2 and preferably between 50 and 90 wt.% silica, with the balance being alumina.